1. Field of the Invention
This invention relates to an improved process for removing oils from oily waste water streams. More particularly, this invention relates to an improved process for removing oil from aqueous refinery streams wherein the oil is present in the stream both as free oil and as an oil-in-water emulsion and is removed from the water by passing the stream through a particulate filter bed of vinyl chloride containing polymers mixed with particles of an inert material. Still more particularly, this invention relates to an improvement in the removal of oil from oily refinery streams wherein the oil is present as a relatively stable oil-in-water emulsion and wherein said streams may be sour water from a steam cracker or spent caustic from steam cracker treating towers which comprises filtering the stream through a filter bed of unprocessed particles of PVC homopolymer or copolymers thereof, the improvement comprising one or more granular, inert filter materials intimately mixed with the polymeric particles in the filter bed.
2. Description of the Prior Art
U.S. Pat. No. 4,008,160, the disclosures of which are incorporated herein by reference, teaches a process for removing oil from oily water streams comprising passing the oily water through a filter bed of granular, unprocessed vinyl chloride containing homopolymers and copolymers. Both free oil and emulsified oil are removed from the water by this process. The oil is actually absorbed by and into the polymeric filter media. This is especially useful for removing oil from the sour water effluent of steam cracker primary fractionator tower overheads, which contain highly olefinic, emulsified and free oil, as well as spent caustic from steam cracked liquid and vapor treating towers which also contains highly reactive, olefinic, polymerizable oil as a stable oil-in-water emulsion.
During commercial use of this process, it was observed that absorption of the oil by and into the polymeric filter media ultimately resulted in softening and swelling of the discrete polymer particles. The soft, expanded, oil-plasticized polymer particles fused to each other resulting in an excessive pressure drop and finally plugging of the filter bed. This occurred at the upstream end of the filter, thereby requiring frequent shutdowns and replacement of the filter media. Further, because the plugging occurred at the upstream end of the filter, replacing the filter media resulted in losing the oil absorption capacity of the polymer particles at the downstream end. Therefore, an improvement to the process was desirable.